Platelet membranes contain neutral glycolipids and acidic glycolipids (gangliosides). These lipids are conceivably critical for platelet functions, e.g., adhesion, aggregation, and serontonin binding. Thrombin induces selective changes in both the amounts of platelet glycosphingolipids and exposure of glycosphingolipids on the platelet surface, possible by altering glycosphingolipid synthesis. The capabilities of human platelet to synthesize glycosphingolipids will be assessed by investigating the precursor-product relationship of platelet glycosphingolipids, through the use of radioactive labeled precursors, e.g., glucose, galactose, and N-acetylmannosamine. Enzymes responsible for the glycosphingolipid synthesis, i.e., glycosyltransferases and sialoyltransferases, will be characterized. The effect of thrombin and other aggregating agents both on the incorporation of precursor into platelet glycosphingolipids and on the transferase activities will also be evaluated. We have shown that the sphingosine composition of human platelet ceramides and glycosphingolipids is different in that the former contain dihydrosphingosine, the latter contains threosphingosine. The structure specificity of sphingosine in the glycolipid synthesis will be studied by using inhibitors, which have a functional group similar to sphingosine, and have isomers with erythro- and threo- configurations, e.g., amides of 1-phenyl-2-amino-1,3-propandiol. The effect of inhibitors on the platelet functions will also be determined. Platelets from patients with platelet disorders in which there is a high probability of abnormal transferase activities, e.g. Fabry's disease, Bernard Soulier syndrome, thrombasthenia, myeloproliferative syndromes, type III hyperlipidemia, will be investigated. The investigation of the specific enzyme activities will be based on the finding of platelet glycosphingolipid composition of these patients. This study should provide information about the role of glycosphingolipids in platelet hemostatic activity and in thrombosis.